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El-Beyrouthy J, Makhoul-Mansour M, Gulle J, Freeman E. Morphogenesis-inspired two-dimensional electrowetting in droplet networks. BIOINSPIRATION & BIOMIMETICS 2023; 18. [PMID: 37074106 DOI: 10.1088/1748-3190/acc779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Accepted: 03/24/2023] [Indexed: 05/03/2023]
Abstract
Living tissues dynamically reshape their internal cellular structures through carefully regulated cell-to-cell interactions during morphogenesis. These cellular rearrangement events, such as cell sorting and mutual tissue spreading, have been explained using the differential adhesion hypothesis, which describes the sorting of cells through their adhesive interactions with their neighbors. In this manuscript we explore a simplified form of differential adhesion within a bioinspired lipid-stabilized emulsion approximating cellular tissues. The artificial cellular tissues are created as a collection of aqueous droplets adhered together in a network of lipid membranes. Since this abstraction of the tissue does not retain the ability to locally vary the adhesion of the interfaces through biological mechanisms, instead we employ electrowetting with offsets generated by spatial variations in lipid compositions to capture a simple form of bioelectric control over the tissue characteristics. This is accomplished by first conducting experiments on electrowetting in droplet networks, next creating a model for describing electrowetting in collections of adhered droplets, then validating the model against the experimental measurements. This work demonstrates how the distribution of voltage within a droplet network may be tuned through lipid composition then used to shape directional contraction of the adhered structure using two-dimensional electrowetting events. Predictions from this model were used to explore the governing mechanics for complex electrowetting events in networks, including directional contraction and the formation of new interfaces.
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Affiliation(s)
- Joyce El-Beyrouthy
- School of Environmental, Civil, Agricultural, and Mechanical Engineering, University of Georgia, Athens, GA, United States of America
| | - Michelle Makhoul-Mansour
- School of Environmental, Civil, Agricultural, and Mechanical Engineering, University of Georgia, Athens, GA, United States of America
- College of Engineering, University of Tennessee Knoxville, Knoxville, TN, United States of America
| | - Jesse Gulle
- School of Environmental, Civil, Agricultural, and Mechanical Engineering, University of Georgia, Athens, GA, United States of America
| | - Eric Freeman
- School of Environmental, Civil, Agricultural, and Mechanical Engineering, University of Georgia, Athens, GA, United States of America
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Challenges and opportunities in achieving the full potential of droplet interface bilayers. Nat Chem 2022; 14:862-870. [PMID: 35879442 DOI: 10.1038/s41557-022-00989-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 05/27/2022] [Indexed: 12/27/2022]
Abstract
Model membranes can be used to elucidate the intricacies of the chemical processes that occur in cell membranes, but the perfectly biomimetic, yet bespoke, model membrane has yet to be built. Droplet interface bilayers are a new type of model membrane able to mimic some features of real cell membranes better than traditional models, such as liposomes and black lipid membranes. In this Perspective, we discuss recent work in the field that is starting to showcase the potential of these model membranes to enable the quantification of membrane processes, such as the behaviour of protein transporters and the prediction of in vivo drug movement, and their use as scaffolds for electrophysiological measurements. We also highlight the challenges that remain to enable droplet interface bilayers to achieve their full potential as artificial cells, and as biological analytical platforms to quantify molecular transport.
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Makhoul-Mansour MM, Challita EJ, Chaurasia A, Leo DJ, Sukharev S, Freeman EC. A skin-inspired soft material with directional mechanosensation. BIOINSPIRATION & BIOMIMETICS 2021; 16:046014. [PMID: 33848998 DOI: 10.1088/1748-3190/abf746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 04/13/2021] [Indexed: 06/12/2023]
Abstract
Lessons about artificial sensor design may be taken from evolutionarily perfected physiological systems. Mechanosensory cells in human skin are exquisitely sensitive to gentle touch and enable us to distinguish objects of different stiffnesses and textures. These cells are embedded in soft epidermal layers of gel-like consistency. Reproducing these mechanosensing capabilities in new soft materials may lead to the development of adaptive mechanosensors which will further enhance the abilities of engineered membrane-based structures with bioinspired sensing strategies. This strategy is explored here using droplet interface bilayers embedded within a thermoreversible organogel. The interface between two lipid-coated aqueous inclusions contained within a soft polymeric matrix forms a lipid bilayer resembling the lipid matrix of cell membranes. These interfaces are functionalized with bacterial mechanosensitive channels (V23T MscL) which convert membrane tension into changes in membrane conductance, mimicking mechanosensitive channel activation in mammalian mechanosensory cells. The distortion of encapsulated adhered droplets by cyclical external forces are first explored using a finite element composite model illustrating the directional propagation of mechanical disturbances imposed by a piston. The model predicts that the orientation of the droplet pair forming the membrane relative to the direction of the compression plays a role in the membrane response. The directional dependence of mechanosensitive channel activation in response to gel compression is confirmed experimentally and shows that purely compressive perturbations normal to the interface invoke different channel activities as compared to shearing displacement along a plane of the membrane. The developed system containing specially positioned pairs of droplets functionalized with bacterial mechanosensitive channels and embedded in a gel creates a skin-inspired soft material with a directional response to mechanical perturbation.
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Affiliation(s)
| | - Elio J Challita
- College of Engineering, University of Georgia, Athens, GA, United States of America
- George W. Woodruff School of Mechanical Engineering, Georgia Tech, Atlanta, GA, United States of America
- School of Chemical & Biomolecular Engineering, Georgia Tech, Atlanta, GA, United States of America
| | | | - Donald J Leo
- College of Engineering, University of Georgia, Athens, GA, United States of America
| | - Sergei Sukharev
- Department of Biology, University of Maryland, College Park, MD, United States of America
| | - Eric C Freeman
- College of Engineering, University of Georgia, Athens, GA, United States of America
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El-Beyrouthy J, Freeman E. Characterizing the Structure and Interactions of Model Lipid Membranes Using Electrophysiology. MEMBRANES 2021; 11:319. [PMID: 33925756 PMCID: PMC8145864 DOI: 10.3390/membranes11050319] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 04/22/2021] [Accepted: 04/25/2021] [Indexed: 11/16/2022]
Abstract
The cell membrane is a protective barrier whose configuration determines the exchange both between intracellular and extracellular regions and within the cell itself. Consequently, characterizing membrane properties and interactions is essential for advancements in topics such as limiting nanoparticle cytotoxicity. Characterization is often accomplished by recreating model membranes that approximate the structure of cellular membranes in a controlled environment, formed using self-assembly principles. The selected method for membrane creation influences the properties of the membrane assembly, including their response to electric fields used for characterizing transmembrane exchanges. When these self-assembled model membranes are combined with electrophysiology, it is possible to exploit their non-physiological mechanics to enable additional measurements of membrane interactions and phenomena. This review describes several common model membranes including liposomes, pore-spanning membranes, solid supported membranes, and emulsion-based membranes, emphasizing their varying structure due to the selected mode of production. Next, electrophysiology techniques that exploit these structures are discussed, including conductance measurements, electrowetting and electrocompression analysis, and electroimpedance spectroscopy. The focus of this review is linking each membrane assembly technique to the properties of the resulting membrane, discussing how these properties enable alternative electrophysiological approaches to measuring membrane characteristics and interactions.
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Affiliation(s)
| | - Eric Freeman
- School of Environmental, Civil, Agricultural and Mechanical Engineering, College of Engineering, University of Georgia, Athens, GA 30602, USA;
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Makhoul-Mansour MM, Freeman EC. Droplet-Based Membranous Soft Materials. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:3231-3247. [PMID: 33686860 DOI: 10.1021/acs.langmuir.0c03289] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Inspired by the structure and functionality of natural cellular tissues, droplet interface bilayer (DIB)-based materials strategically combine model membrane assembly techniques and droplet microfluidics. These structures have shown promising results in applications ranging from biological computing to chemical microrobots. This Feature Article briefly explores recent advances in the areas of construction, manipulation, and functionalization of DIB networks; discusses their unique mechanics; and focuses on the contributions of our lab in the advancement of this platform. We also reflect on some of the limitations facing DIB-based materials and how they might be addressed, highlighting promising applications made possible through the refinement of the material concept.
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Affiliation(s)
- Michelle M Makhoul-Mansour
- School of Environmental, Civil, Agricultural and Mechanical Engineering, University of Georgia, Athens, Georgia 30602, United States
| | - Eric C Freeman
- School of Environmental, Civil, Agricultural and Mechanical Engineering, University of Georgia, Athens, Georgia 30602, United States
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Lee CF, Wang MR, Lin TL, Yang CH, Chen LJ. Dynamic Behavior of the Structural Phase Transition of Hydrogel Formation Induced by Temperature Ramp and Addition of Ibuprofen. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:8929-8938. [PMID: 32654495 DOI: 10.1021/acs.langmuir.0c01437] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Understanding the dynamic behavior of hydrogel formation induced by a temperature ramp is essential for the design of gel-based injectable formulation as drug-delivery vehicles. In this study, the dynamic behavior of the hydrogel formation of Pluronic F108 aqueous solutions within different heating rates was explored in both macroscopic and microscopic views. It was discovered that when the heating rate is increased, the gelation temperature window (hard gel region) shrinks and the mechanical strength of the hydrogel decreases. A given system at different heating rates would lead to different crystalline structural evolutions. The time-resolved small-angle X-ray scattering (SAXS) experiments at a heating rate of 10 °C/min disclose that the crystalline structure of micelle packing in the hydrogel exhibits a series of transitions: hexagonal close-packed (HCP) to face-centered cubic (FCC) and body-centered cubic (BCC) structures coexisting and then to the BCC structure along with the increasing temperature. For the system at equilibrium, the BCC structure exclusively dominates the system. Furthermore, the addition of a hydrophobic model drug (ibuprofen) to the F108 aqueous solution promotes hard gel formation at even lower temperatures and concentrations of F108. The SAXS results for the system with ibuprofen at a heating rate of 10 °C/min demonstrate a mixture of FCC and BCC structures coexisting over the whole gelation window compared to the BCC structure that exclusively dominates the system at equilibrium. The addition of ibuprofen would alter the structural evolution to change the delivery path of the encapsulated drug, which is significantly related to the performance of drug release.
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Affiliation(s)
- Chin-Fen Lee
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Mu-Rong Wang
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Tsang-Lang Lin
- Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Ching-Hsun Yang
- Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Li-Jen Chen
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
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Makhoul-Mansour MM, El-Beyrouthy JB, Mumme HL, Freeman EC. Photopolymerized microdomains in both lipid leaflets establish diffusive transport pathways across biomimetic membranes. SOFT MATTER 2019; 15:8718-8727. [PMID: 31553025 DOI: 10.1039/c9sm01658a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Controlled transport within a network of aqueous subcompartments provides a foundation for the construction of biologically-inspired materials. These materials are commonly assembled using the droplet interface bilayer (DIB) technique, adhering droplets together into a network of lipid membranes. DIB structures may be functionalized to generate conductive pathways by enhancing the permeability of pre-selected membranes, a strategy inspired by nature. Traditionally these pathways are generated by dissolving pore-forming toxins (PFTs) in the aqueous phase. A downside of this approach when working with larger DIB networks is that transport is enabled in all membranes bordering the droplets containing the PFT, instead of occurring exclusively between selected droplets. To rectify this limitation, photopolymerizable phospholipids (23:2 DiynePC) are incorporated within the aqueous phase of the DIB platform, forming conductive pathways in the lipid membranes post-exposure to UV-C light. Notably these pathways are only formed in the membrane if both adhered droplets contain the photo-responsive lipids. Patterned DIB networks can then be generated by controlling the lipid composition within select droplets which creates conductive routes one droplet thick. We propose that the incorporation of photo-polymerizable phospholipids within the aqueous phase of DIB networks will improve the resolution of the patterned conductive pathways and reduce diffusive loss within the synthetic biological network.
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Affiliation(s)
- Michelle M Makhoul-Mansour
- School of Environmental, Civil, Agricultural and Mechanical Engineering, University of Georgia, Athens, Georgia 30602, USA.
| | - Joyce B El-Beyrouthy
- School of Environmental, Civil, Agricultural and Mechanical Engineering, University of Georgia, Athens, Georgia 30602, USA.
| | - Hope L Mumme
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - Eric C Freeman
- School of Environmental, Civil, Agricultural and Mechanical Engineering, University of Georgia, Athens, Georgia 30602, USA.
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